Macintosh IIfx

My unit comes from Germany, and that's all I know. It was previously opened and video board has been upgraded, as well as hard disk controller for some external drive.
The mainboard is quite strange. It works, and replacing bad capacitors made it work more stable, but it has a strange RAM sockets - all of them are black except one, which is white. In most photos there are mainboards with a complete set of sockets in a single color. And it has not been made by service - it is factory-soldered. The mainboard is the one with most decoupling capacitors made on tantalum, but earlier revisions could have a small SMD electrolytic caps which could leak. It is recommended to inspect capacitors before running this type of Mac.

Batteries and power-up

The IIfx has two sockets for 3.6V lithium batteries and both of them are needed to start a computer. These batteries power a flip-flop which allows to feed some voltage to power supply unit which, in turn, flips a relay and starts up. One battery is used only to maintain NVRAM. This is quite complicated start-up circuit and it is quite probable that it may cause some problems. The power supply has its power-on line and it needs some voltage on it to start.
So batteries are crucial for this thing to start up. It is possible to start it up from two CR2032 batteries with adapter, but don't insert batteries when power is connected or it may unexpectedly start up.
The question that goes on by itself is WHY? This circuit, described in many places over Internet (Gamba's site, Startup explanation blog post in links section of this page) is certainly overengineered. I have no idea why they had to use such thing, especially that they already had a nice ground-only working version of power supply used in earlier Macs. There are however several explanations:
- They already had the power supply unit made this way and it was needed to use it,
- The primary design of the casing was for some expansion box for other Macs which powered up when Mac fed its power there,
- They, like Olivetti, considered a machine which could be remotely turned on by phone line and send the data at night to some computer center. However with Apple's ideas in their modems it's not much probable - Although quite reluctant in developing networking in the beginning of Macintosh line, Apple finally got a nice idea around their interface and transceivers.
- They wanted to prevent starting up without NVRAM good. This is also possible as video board in this Mac tends to crash the computer if proper monitor definition is not stored in NVRAM.
So here is only to guess.

Easter egg To see the picture:  - Set the system date to 19 March 1990 (Mac IIfx's release date)  - Restart with Command-Option-F-X pressed From here. The picture is in ROM, so it's not dependent on installed or booted operating system, only the date is important. Clicking will retry a normal system startup.

Disassembly

Quite simple. One screw on the rear, press levers, open the top cover towards front and after quite large angle it should unlatch. The drive shelf is kept with a few screws. RAM and batteries are under it. If you unplug HDD it is possible to just flip it onto power supply. Hard drive is located on the shelf and it is usually belly-up, so if you upgrade remember about possibility to mount HDD with electronics on top. Also, some chassis have their mounting holes not exactly in standard alignment - literally 2-2,5mm.

Supermac video board

The video board - SuperMac Spectrum 24 IV, is quite nice accelerator capable of 24-bit color in high resolutions, but has one problem: It relies on computer's PRAM to keep display settings. So it starts, by default, in some incompatible resolution and it is needed to set the proper one. You may need drivers and manual too.

To set the proper resolution, boot the computer (doesn't matter hard disk or floppy) and hold OPTION key during boot. In some stage, and it's quite late stage after "Welcome..." screen, the screen will change to a keyboard image with blinking space, sometimes with resolution shown above. The resolutions and screen modes will change, depending on ROM slower or faster (in my ROM 1.7.2 it's quite fast). When the resolution is OK, press space. The board will write value into PRAM and restart. This of course becomes forgotten when battery runs out or you zap the PRAM. The monitor switch settings are interpreted weirdly and if a VGA converter with jumpers/switches is used, it's better to select "Multi Res" type monitor. This may fallback to monochrome (can be set from control panel), but will give some certain resolution.

Links

https://www.swiat-owocow.pl/?issue=komputer.7.90&article=sprinter - Review in Polish from KOMPUTER Magazine
http://www.storiesofapple.net/the-mac-iifx-apple-enters-the-workstation-market.html - According to this info they designed it as UNIX workstation.
http://www.mathdittos2.com/columns/bh/bh990511.html - Description from Mac IIfx owner
https://www.oldcomputr.com/restoring-an-apple-macintosh-ii/ - Restoration of Mac II with nice photos.
https://www.downtowndougbrown.com/2015/03/explanation-of-the-macintosh-iiiix-power-onoff-circuit/ - A description of power circuit
http://web.archive.org/web/20131031134159/http://home.earthlink.net/~gamba2/ - Gamba2's page with technical information
http://lowendmac.com/video/spectrum24siv.html - SuperMac Spectrum 24 IV information.
http://web.archive.org/web/20180103184539/http://home.earthlink.net/~gamba2/vid-mon-matrix.html - SuperMac information from Gamba, unfortunately download links gone.
http://radius.vintagebox.de/RadiusQA/Spectrum.html - Spectrum video boards Q/A.